Method for applying an internal coating to a cathode ray tube

ABSTRACT

Apparatus for applying Adquadag coating to the funnel of a cathode ray tube envelope comprises means for supporting the envelope with the sealing land exposed, and means for spraying an Aquadag solution upon the wall of the funnel. A deflector is interposed between the spray means and the edge of the funnel to intercept that portion of the spray directed toward that edge while another member is positioned adjacent the inside wall of the funnel to establish an orifice between that member and that portion of the funnel wall normal to the sealing land. The envelope supporting means is rotated, relative to the spray means, to apply a uniform coat of Aquadag upon the funnel while an air pump establishes a pressure differential between the inside of the envelope and the outside to generate a flow of air across the sealing land of the funnel, up through the orifice and into the funnel to prevent deposit of coating material upon the sealing land. The invention also contemplates a method, utilizing the above described apparatus, for applying an Aquadag material to the funnel section of a cathode ray tube while maintaining the sealing land free of material.

I United States Patent Nuehring [4 1 Feb. 12, 1974 METHOD FOR APPLYING AN INTERNAL COATING TO A CATHODE RAY TUBE- Donald E. Nuehring, Chicago, Ill.

[73] Assignee: Zenith Radio Corporation, Chicago,

[22] Filed: Feb. 2, 1972 [2]] Appl. No.: 222,874

[75] Inventor:

Primary ExaminerRalph Husack Attorney, Agent, or FirmCorne1ius J. OConnor; John J. Pederson Exhoust i Sourceof l 5 7 1 ABSTRACT Apparatus for applying Adquadag coating to the fun nel of a cathode ray tube envelope comprises means for supporting the envelope with the sealing land exposed, and means for spraying an Aquadag solution upon the wall of the funnel. A deflector is interposed between the spray means and the edge of the funnel to intercept that portion of the spray directed toward that edge while another member is positioned adjacent the inside wall of the funnel to establish an orifice between that member and that portion of the funnel wall normal to the sealing land. The envelope supporting means is rotated, relative to the spray means, to apply a uniform coat of Aquadag upon the funnel while an air pump establishes a pressure differential between the inside of the envelope and the outside to generate a flow of air across the sealing land of the funnel, up through the orifice and into the funnel to prevent deposit of coating material upon the sealing land. The invention also contemplates a method, utilizing the above described apparatus, for applying an Aquadag material to the funnel section of a cathode ray tube while maintaining the sealing land free of material.

3 Claims, 5 Drawing Figures 33 2s s H 29 3 l l l l c i 3 PATENTEDFEB'I 21914 sum 1 0F 2 Exhaust Sou rce of Aqucldug i PAIENIE rm I 2 m4 SHEEI 2 OF 2 FIG. 3

METHOD FOR APPLYING AN INTERNAL COATING TO A CATHODE RAY TUBE BACKGROUND OF THE INVENTION This invention relates in general to the manufacture of cathode ray tubes and in particular to apparatus and a method for applying a coating to the envelope of a color reproducing cathode ray tube.

A conventional color tube comprises a face panel, upon which a myriad of red, green and blue phosphor dots are screened, and an envelope comprising a funnel section which includes a neck section that supports a trio of electron beam generating for exciting the phosphor dots. Since the funnel and face panel are ultimately joined, each is provided with a flat sealing land of substantially identical contour and surface area.

One of the initial steps performed in the processing of the funnel section entails the application of a coating of Aquadag to the internal surface of the funnel either by spraying or by painting. This coating serves as a conductor for applying high voltage to the final or accelerating anodes of the electron guns as well as one electrode of a filter capacitor for the high voltage supply. As already noted, the funnel section must be joined to a screened face panel, therefore care must be exercised when applying the Aquadag in order to prevent any of that material from being deposited upon the sealing land of the funnel. To achieve this end one prior art approach is to cover the sealing land with a mask or a piece of tape which is removed after the coating operation. The economic shortcomings of this practice, both as to material and labor, are obvious.

After the face panel has been screened and the funnel section coated with Aquadag, the respective sealing lands of the face panel and the funnel section are joined by a frit sealing process which permanently bonds these two portions of the envelope. The tube is then provided with an electron gun arrangement which substantially completes the manufacturing process of a color reproducing tube. Thereafter, when a tube of this type is employed in a television receiver the final anodes of the electron gun arrangement, as well as the internal Aquadag coating, are maintained at a very high accelerating voltage, potentials in the order of 22KV to 25 KV being commonly used, depending upon the size of the picture tube.

With potentials of the aforementioned magnitude established on the internal Aquadag surface of the funnel, it now becomes apparent why precaution must be excerised in applying the Aquadag material to the funnel. More particularly, when the tube is mounted upon a chassis the frit seal section of the tube envelope is usually located near a surface maintained at ground potential so that an electric potential is developed across the frit seal commensurate in magnitude with the order of the voltage applied to the final anode. Accordingly, since Aquadag is conductive, even a minute deposit of that material upon the sealing land of the funnel greatly enhances the possibility of an arc through the frit seal to a nearby ground plane. This arc-over or punchthrough is usually of such a destructive nature as to render the tube a reject.

Accordingly, it is an object of the invention to provide improved apparatus for applying a coating to the funnel section of a cathode ray tube.

It is another object of the invention to provide apparatus for confining a conductive coating to a restricted surface of the funnel section of a cathode ray tube.

It is a specific object of the invention to provide Aquadag spray coating apparatus which precludes deposit of Aquadag upon the sealing land of the funnel section of the tube.

It is a further object of the invention to provide an improved method of applying a coating to the funnel section of a cathode-ray tube envelope.

It is also a specific object of the invention to provide a method of spray coating a cathode-ray tube funnel which precludes deposit of the coating material upon the sealing land of the funnel.

SUMMARY OF THE INVENTION The invention pertains to apparatus for applying an internal coating to the funnel section of a cathode ray tube envelope, which section has an edge portion that terminates in a sealing land. The apparatus comprises means for supporting the tube envelope with substantially the entire surface of the sealing land exposed, and means for directing a spray of coating material toward the inside wall of the funnel. A deflector is interposed between the spray means and the edge portion of the funnel section to directly intercept the spray material directed toward the edge portion while another member is positioned adjacent the inside wall of the edge portion to establish an orifice between that member and that portion of the funnel wall normal to the sealing land. Means are included for effecting a relative rotation between the spray means and the envelope supporting means so as to apply the coating material uniformly upon the portion of the funnel wall extending between the deflector and the neck section. Finally, means are provided for establishing a pressure differential between the inside of the envelope and the outside so as to generate a flow of air across the sealing land, up through the orifice and into the funnel to prevent deposit of the coating material upon the sealing land.

The invention further contemplates a method for applying a coating on the inside wall of the funnel section of a color tube envelope which method contemplates supporting the envelope with substantially the entire surface of its sealing land exposed and then directing a spray of coating material toward the inside wall of the funnel. Simultaneously, while a relative rotation is effected between the spray means and the envelope supporting means to apply coating material uniformly upon the funnel wall, that portion of the spray material directed toward the edge portion of the funnel is directly intercepted, and a pressure differential is developed between the inside of the envelope and the outside thereof to generate a flow of air through an orifice surrounding the inside wall of the edge portion of the funnel to prevent deposit of coating material upon the sealing land.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with further objects and advantages thereof may best be understood by reference to the following description taken in conjunction with the accompanying drawings, in the several figures of which like reference numerals identify like elements and in which:

FIG. 1 is an elevational view, partly in section, of an apparatus for applying a coating to the inside wall of the funnel section of a cathode ray tube envelope;

FIG. la is a perspective view detailing one of the tube envelope support posts shown in FIG. 1;

FIG. 2 is a sectional view taken along lines 22 of FIG. 1;

FIG. 3 is a sectional view taken along lines 33 .of a portion of the apparatus shown in FIG. 2; and

FIG. 4 is a fragmentary perspective view of one corner of the envelope supporting apparatus shown in FIGS. 1 and 2.

The apparatus shown in FIG. 1 is employed to apply a coating of Aquadag to a restricted area on the inside wall of the funnel section of a color cathode ray tube. As previously noted, a color reproducing cathode ray tube is comprised of a screened face panel (not shown) which is eventually mated to an envelope 11. This envelope comprises a neck section 12 and a funnel section 13. As best seen in FIG. 3, funnel section 13 has an edge portion 14 which terminates in a sealing land 15. This sealing land is a substantially flat surface and exhibits substantially the same contour and area as that presented by the sealing land of the face panel to which it is subsequently joined.

Envelope 11 is supported with neck section 12 uppermost, and with substantially the entire surface of sealing land 15 exposed, by a plurality of posts 17 each of which includes a foot 18 that presents a reduced sur-' face area to the sealing land. In this manner the sealing land is in limited contact with the support foot and, as shown in the disclosed embodiment, at six widely separated points. As a result substantially the entire surface of the sealing land is exposed to the surrounding atmosphere. Posts 17 further comprise a tapered portion 19 which serves to guide and direct the funnel 13 onto the support feet 18.

Posts 17, in turn, are affixed to an annular ring 20 which is secured within a flange 21 that surmounts a conical shaped chamber 22. This chamber is affixed to a centrally relieved core member 23 which is rotatably supported by a pair of conventional ball race assemblies 24, 25. The lower extremity of core member-23 is provided with a groove 26 for receiving a drive belt 27, which belt encircles the drive pulley 28 of an electric motor 29.

Communicating with the bottom of core 23 is a plenum chamber 30 that presents an opening 31 to the impeller 32 of an exhaust fan 33. An adjustable valve 34, which effectively comprises an air by-pass in shunt with core member 23, is arranged to control the amount of air drawn by impeller 32 through chamber 22 and core member 23.

The means for directing a spray of coating material toward the inside wall of funnel section 13 comprises a dual nozzle sprayhead 35 which is supported atop an inlet conduit 36 that extends through core member 23 and plenum chamber 31 to a support pedestal 37. Another conduit 38 couples a source of Aquadag to. the inlet of pedestal 37.

Interposed between the spray nozzle 35 and the inside wall of funnel section 13 is a deflector 40, see FIG. 3, which directly intercepts the coating material issuing from the spray nozzle to shield the inside of edge portion 14 of the funnel. Positioned adjacent the inside wall of edge portion 14 is a collar 42 which is spaced from the inside wall, see FIG. 3, a distance sufficient to establish an orifice between that collar and the inside wall of the funnel. Preferably, collar 42 and deflector 40 are formed as an integral ring or gasket 43 which surrounds the inner perimeter of edge portion 14 of the funnel. As best seen in FIG. 4 gasket 43 includes a series of drain holes 44 for draining off any Aquadag coating material that collects between the collar 42 and deflector 40.

The purpose of collar 42 is to establish an orifice for directing a flow of air from outside the tube envelope across the surface of sealing land 15 and into the funnel. This air flow is established by the creation of a pressure differential between the inside of the envelope and the outside, specifically by exhaust fan 33 and plenum chamber 31 located at the bottom of core member 23. The role of control valve 34 is now more readily understandable in that opening of this valve effectively shunts or reduces the amount of air drawn through the orifice established between collar 42 and the inside wall of edge portion 14 of the funnel. In this fashion the amount of air drawn across the sealing land is directly controllable by adjusting the position of valve 34.

As shown in FIG. 1 a plug 45 is inserted in the neck section 12 of the envelope. The purpose of this plug is to prevent any of the Aquadag spray from entering the neck of the envelope. More particularly, in some cases it is desirable to apply a precisely defined coating of Aquadag inside the neck prior to coating the funnel wall. This could be the instance where a short-necked tube is being processed and it would be undesirable to have Aquadag material extending beyond a precisely defined boundary. On the other hand where a long necked tube, or some other consideration is presented, it is permissible or even desirable to omit plug 45. In this latter situation the amount of Aquadag spray entering the neck of the tube is controlled by the inrush of air drawn down the neck by exhaust fan 33.

In the operation of the subject apparatus, the motor 29 is energized to rotate the envelope supporting means comprising core 23 and cone 22 at a predetermined rate of velocity. At the same time exhaust fan 33 is energized and valve 34 adjusted to control the flow of air across sealing land 15 of the envelope. With the envelope rotating and air flowing across the sealing land and through the orifice defined by collar 42, nozzles 35 are opened to discharge a pair of fan-shaped sprays against the inside wall of the funnel. One of the nozzles serves to spray the upper portion of the funnel wall to a point that includes the neck section. However, as shown in FIG. I, plug 45 prevents Aquadag material from entering the neck section itself. The second nozzle develops a spray which overlaps a portion of the area covered by the first nozzle and extends downward toward the lower edge of the funnel wall. However, the sealing land of the funnel is protected by the conjoint action of the deflector 40 and the orifice established by collar 42. More particularly, deflector 40 serves to directly intercept the spray of material from the lower nozzle so as to prevent it from impinging upon the inside wall of portion 14 of the funnel. Secondly, the inrush current of air across sealing land '15 generated by the exhaust fan is driven up and over the collar 42 thereby preventing any Aquadag material from descending into the area of the funnel wall immediately adjacent the sealing land. As a result, Aquadag material is prevented from being deposited on the sealing land. Accordingly, by resort to the described apparatus, an Aquadag coated funnel requires only an abbreviated drying period prior to its next processing step as no cleansing step is required to remove Aquadag material from the sealing land.

While the disclosed embodiment shows spray means 35 maintained in a fixed position while the envelope is rotated relative thereto, it is recognized that the reverse operation can be employed. Specifically, the envelope supporting means can be maintained stationary and the Aquadag spray nozzles rotated relative to the envelope.

Finally, it is appreciated that the invention contemplates the method of coating the funnel section of a cathode ray tube envelope employing the abovedescribed apparatus.

While a particular embodiment of the invention has been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects and, therefore, the aim in the appended claims is to cover all such changes and modifications as fall within the'true spirit and scope of the invention.

I claim:

1. A method for applying a coating to the wall of a cathode ray tube envelope that comprises a neck section and a funnel section having an edge portion that terminates in a sealing land, said method comprising the following steps:

supporting said envelope with substantially the entire surface of said sealing land exposed;

directing a spray of coating material toward the inside wall of said funnel section;

shielding the edge portion of said funnel section from said coating material by directly intercepting said spray of coating material;

establishing an orifice adjacent the inside wall of the edge portion of said funnel for directing a flow of gas across said sealing land;

effecting relative rotation between said spray of coating material and said envelope to apply said coating material upon that portion of said funnel wall extending between the shielded edge portion of the funnel and said neck section;

and establishing a pressure differential between the inside of said envelope and the outside thereof to generate a flow of gas across said sealing land, through said orifice and into said funnel to prevent deposit of coating material upon said sealing land.

2. The method for applying a coating to the wall of a cathode ray tube envelope as set forth in claim 1 in which said envelope is rotated relative to said spray of coating material.

3. The method for applying a coating to the wall of a cathode ray tube envelope as set forth in claim 1 in which a flow of gas through said neck section is addi tionally generated to prevent deposit of coating material inside said neck section. 

2. The method for applying a coating to the wall of a cathode ray tube envelope as set forth in claim 1 in which said envelope is rotated relative to said spray of coating material.
 3. The method for applying a coating to the wall of a cathode ray tube envelope as set forth in claim 1 in which a flow of gas through said neck section is additionally generated to prevent deposit of coating material inside said neck section. 